I found the FM Pad in Reason's NN-XT sampler to be a pretty nice start for deep house. Of course this doesn't help if you don't have Reason. Sine based pads are nice but most presets these days have a bit much going on in the upper frequency range for deep house. Same with organs. So low-pass filter that shit just a bit, add a dash of resonance and off you go!

Hi , you can try a lot of synth in fact but play with the enveloppe make a longer attack and use some minor seven chords ...i'am not an expert but i very often try to make those sexy house chords electric pianos can give some good results too.